Stabilizing emulsions

ABSTRACT

A method of stabilizing a water-in-oil emulsion, comprising the steps of: 
     a) preparing a composition comprising oil, water, and a silane having bonds that hydrolyse and condense to form a cross-linked polymer, thereby creating a dispsersed aqueous phase in a continuous oil phase; 
     b) allowing the silane to hydrolyse; 
     c) allowing the hydrolysed silane to condense to form a crosslinked polymer at an interface between the oil and the aqueous phase, thereby encapsulating the dispersed aqueous phase.

The present invention relates to stabilising emulsions, and concerns inparticular a method for stabilising water-in-oil emulsions suitable foruse in oil-based drilling muds.

When drilling a well, specifically an oil well, a drilling mud isemployed primarily to carry rock cuttings up to the surface and out ofthe wellbore. Other functions of the mud are to cool and lubricate thedrill bit, to protect against blowouts by counteracting downholeformation pressure, to maintain a stable borehole, and to prevent lossof fluids to the formations being drilled. Both water-based andoil-based muds are used as drilling muds. Water-based muds (WBMs) aregenerally cheaper than oil-based muds (OBMs), but the latter possessmany operational advantages, particularly for the drilling of highangle, long reach and high pressure/high temperature wells. However,conventional oil-based muds do suffer from a number of undesirablecharacteristics. For example, the oil may be retained on the drillcuttings, which has unfortunate environmental implications. In addition,the presence of emulsifiers and other oil wetting agents, which areessential components of conventional OBMs (these are usually emulsionsof water in oil, and the emulsifiers and wetting agents keep theemulsions stable and useful), can alter the wettability of oil-holdingreservoir formations through which the borehole passes, thereby reducingtheir permeability to oil, and so making it more difficult to extractthe oil therefrom.

Emulsifiers and oil wetting agents are added to conventional OBMs toemulsify the water phase in the oil phase, and to ensure that all of thesolids in the mud are wetted by the oil. Surfactants, solids at theinterface, or polymers can be used to stabilise such emulsions, and highlevels of water can be stabilised in such muds, whilst maintaining allthe other properties required of an oil-based mud, provided thatsufficient surfactant is present. Now, the amount of oil in the mud andthe oil wetting characteristics of the mud are important parametersaffecting the concentration of oil retained on drilling cuttings, andunfortunately the high levels of surfactant often required result inundesirably strong oil wetting characteristics. The present inventionseeks to provide an alternative way of preparing water-in-oil emulsionsso that in such emulsions high water levels and high stability can stillbe achieved but with the use of minimal levels of surfactant. Morespecifically, the invention suggests that the stability of water-in-oilemulsions may be significantly enhanced by using as a stabilising agenta particular type of silane--thus, first there is formed a water-in-oilemulsion with a fine dispersed aqueous phase in the continuous oilphase, and then there is added to this a silane having bonds whichhydrolyse and condense to form a cross-linked polymer at the water-oilinterface.

Thus, according to the present invention there is provided a method forenhancing the stability of a water-in-oil emulsion, in which methodthere is added to the emulsion a silane having bonds which are capableof hydrolysing and condensing whereby a cross-linked silicone is formedat the interface between the oil and the water, thereby encapsulatingthe water droplets and so stabilising the emulsion.

In a second aspect, the invention provides a method for forming a stablewater-in-oil emulsion, in which method:

a) first there is formed a fine dispersed aqueous phase within acontinuous oil phase, this being the desired water-in-oil emulsion; andthen

b) there is added to the emulsion a silane having bonds which arecapable of hydrolysing and condensing whereby a cross-linked silicone isformed at the interface between the oil and the water, therebyencapsulating the water droplets and so stabilising the emulsion.

The water-in-oil emulsion can be prepared in any convenient way suitablefor making a fine dispersion of an aqueous phase in a continuous oilphase, but preferably it is prepared by strong physical agitation of theaqueous and oil components in the presence of a suitable water-in-oilemulsifier.

Suitable emulsifiers include fatty acid soaps such as calcium dioleate,fatty amides such as the reaction products of oleic acid anddiethylamine thiamine, a variety of polymeric emulsifiers containingalcohol or carboxylic acid groups or organophilic clays, and certainorganic-silicone-based polymers. Such polymers can be the cross-linkedorganosilicone polymers disclosed in EP 0,298,402, but the preferredemulsifiers are silicone copolymers having a silicone backbone withpendant hydrophobic alkyl chains and pendant ethylene oxide/propyleneoxide chains, as typified by that material known as TEGOPREN 7006supplied by Th. Goldschmidt. This is believed to be an alkyl- andpolyether-modified siloxane.

Naturally, the emulsifiers should be present at low concentrations;0.5-50 g/l of emulsion seems acceptable.

Suitable silanes for use in the method of the present invention arethose of the General Formula:

    R.sub.4-n --Si--X.sub.n                                    (I)

(wherein

R represents a straight- or branched-chain alkyl group containing from 1to 18 carbon atoms, or an aryl group,

X represents a R'O--, R'COO--, R'NH--, R'₂ N--, R'═NO-- or HO-- group,or a halogen atom, and

R' represents a straight- or branched-chain alkyl group containing from1 to 8 carbon atoms, or an aryl group), and

n is 1-3);

or of the General Formula: ##STR1## (wherein Y and Z represent R, R' orX, as just defined, and

m is 0-100).

A particularly preferred silane is methyl-trimethoxy-silane (a compoundof General Formula I wherein R is the methyl group, n is 3, and each Xis a methoxy group).

These silanes may be used at any convenient concentration; one in therange from 0.5 to 20 g/l of emulsion seems most suitable.

The silane employed is one that hydrolyses and condenses in use. Ifrequired, a suitable catalyst--for example, an alkali such as sodiumhydroxide--may be present in the aqueous phase during the addition ofthe silane, or alternatively an appropriate catalyst--such as anorganometallic catalyst, or a metal, or metal halide, such as tin, orzinc chloride--may be present in the oil phase.

The method of the present invention is particularly suitable forstabilising emulsions which have a high water content--for example,those with an oil/water creation of up to 40/60.

By means of the methods of the present invention water droplets may beencapsulated by the cross-linked silicone, thereby isolating the waterfrom the oil and so reducing the tendency for droplet coalescence whichcan lead to emulsion instability.

Although discussed here in relation to the drilling of oil wellboreholes, the methods of the present invention are suitable forenhancing the stability of any water-in-oil emulsion, and other examplesof these are those for use in cosmetics, in paints or in theoil-refining industry. However, the methods are particularly suitablefor use in the preparation of oil-based drilling muds--OBMs--which shownon-oil-wetting characteristics and acceptable rheological properties.

The present invention is further illustrated by reference to thefollowing Example, which describes the preparation of a stabilisedemulsion having an oil/brine ratio of 50:50.

EXAMPLE

1 g of TEGOPREN 7006 (supplied by Th. Goldschmidt) was dissolved in 175ml kerosene (BP 83 HF, from BP Chemicals), with minimal mixing. 175 mlof calcium chloride brine was then emulsified into the kerosene usingeither a Hamilton Beach mixer or a Ystral high shear blender, and theresultant emulsion allowed to cool to room temperature.

After cooling, 3 g of methyl-trimethoxy-silane was added in a short butvigorous mixing procedure, and the resultant emulsion was left forapproximately 30 mins to allow cross-linking to take place.

The final emulsion this formed was stable, and suitable for use as adrilling fluid.

What is claimed is:
 1. A method of stabilizing a water-in-oil emulsion,comprising the steps of(a) preparing a composition comprising oil,water, and a silane having bonds that hydrolyse and condense to form across-linked polymer, thereby creating a dispersed aqueous phase in acontinuous oil phase; (b) letting said silane hydrolyse; (c) lettingsaid hydrolysed silane condense to form a crosslinked polymer at aninterface between said oil and said aqueous phase, thereby encapsulatingsaid dispersed aqueous phase.
 2. The method of claim 1, in which thewater-in-oil emulsion is prepared by physical agitation of the aqueousand oil components in the presence of a suitable water-in-oilemulsifier.
 3. The method of claim 2, in which the emulsifier is asilicone copolymer having a silicone backbone with pendant hydrophobicalkyl chains and pendant ethylene oxide/propylene oxide chains.
 4. Themethod of claim 2, in which the emulsifier is present at a concentrationof from 0.5 to 50 g/l of emulsion.
 5. The method of claim 1, in whichthe silane is of the General Formula:

    R.sub.4-n --Si--X.sub.n                                    (I)

wherein R represents a straight- or branched-chain alkyl groupcontaining from 1 to 18 carbon atoms, or an aryl group, X represents aR'O--, R'COO--, R'NH--, R'₂ N--, R'═NO-- or HO-- group, or a halogenatom, and R' represents a straight- or branched-chain alkyl groupcontaining from 1 to 8 carbon atoms, or an aryl group, and n is 1-3;orof the General Formula: ##STR2## wherein Y and Z represent R, R' or X,as just defined, and m is 0-100.
 6. The method of claim 5, in which thesilane is methyl-trimethoxy-silane.
 7. The method of claim 1, in whichthe silane is used at a concentration of from 0.5 to 20 g/l of emulsion.